Brunei Shell Petroleum offshore well A was offline andrnshut in due to the 3 1/8" 5K lower master valve on thernmonoblock tree, being seized in the closed position, duernto scale production. The subsequent loss of productionrnwas 200 m3 (1260 BOPD), with a monetary value ofrnUS$1.5 million per month at $40 per barrel.rnTwo options were considered for recovering the wellrnusing well intervention techniques rather than arncomplete workover and well killing operation.rn1. Mobilize a "Gate Valve Milling Machine" the nearestrnbeing available was in Europe.rn2. Mill the Gate Valve with a coiled tubing unit, whichrnwas already on the platform, performing a stimulationrnprogramme on adjoining wells.rnOption one was expensive due to high mobilizationrncosts, some HSE issues, well control but this was a triedrnand test method of remedying the problem. Option twornwas a somewhat untried operation, which had only beenrnperformed as far as BSP and the contractors involvedrnknew, once before in the North Sea.rnGiven the coiled tubing unit was already on the platform,rnand the specialist low speed high torque motors with anrnanti stall device and specialist mills were availed in therntime frame required. The decision process based onrnHSE, engineering review (SWOP), and costrnconsiderations, chose the coiled tubing option.rnThe paper will examine the problem with the wellheadrnmaster valve, the HSE, engineering and cost decision process leading up to the decision to go with the coiledrntubing option. The milling operation from programmerninception to successful execution of the millingrnoperation, and placing the well back on line, will reviewrnin detail.rnOther operators will be able to benefit from this safe, lowrncost and time saving method of recovering productionrnfrom wells with similar problems, which are many aroundrnthe world.
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